Crystal structure of tetraaquabis(pyrimidin-1-ium-4,6-diolato-κO4)manganese(II)

The MnIIion in the structure of the mononuclear title compound, [Mn(C4H3N2O2)2(H2O)4], is situated on an inversion center and is coordinated by two O atoms from two deprotonated 4,6-dihydroxypyrimidine ligands and by four O atoms from water molecules giving rise to a slightly distorted octahedral coordination sphere. The complex includes an intramolecular hydrogen bond between an aqua ligand and the non-protonated N ring atom. The extended structure is stabilized by intermolecular hydrogen bonds between aqua ligands, by hydrogen bonds between N and O atoms of the ligands of adjacent molecules, and by hydrogen bonds between aqua ligands and the non-coordinating O atom of an adjacent molecule.

Controlled translocation of palladium(ii) within a 22 ring atom macrocyclic ligand

Palladium can be directed to coordinate to the “tail” region of the macrocycle H4L to give 3b. Translocation of the palladium from the tail coordination pocket to the head coordination pocket occurs on treatment with amines such as n-BuNH2 to give 4.

Methyl 4-O-β-D-mannopyranosyl β-D-xylopyranoside

Methyl β-D-mannopyranosyl-(1→4)-β-D-xylopyranoside, C12H22O10, (I), crystallizes as colorless needles from water, with two crystallographically independent molecules, (IA) and (IB), comprising the asymmetric unit. The internal glycosidic linkage conformation in molecule (IA) is characterized by a φ′ torsion angle (O5′Man—C1′Man—O1′Man—C4Xyl; Man is mannose and Xyl is xylose) of −88.38 (17)° and a ψ′ torsion angle (C1′Man—O1′Man—C4Xyl—C5Xyl) of −149.22 (15)°, whereas the corresponding torsion angles in molecule (IB) are −89.82 (17) and −159.98 (14)°, respectively. Ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH2OH) C atom in the β-Xylpand β-Manpresidues, respectively. By comparison, the internal glycosidic linkage in the major disorder component of the structurally related disaccharide, methyl β-D-galactopyranosyl-(1→4)-β-D-xylopyranoside), (II) [Zhang, Oliver & Serriani (2012).Acta Cryst.C68, o7–o11], is characterized by φ′ = −85.7 (6)° and ψ′ = −141.6 (8)°. Inter-residue hydrogen bonding is observed between atoms O3Xyland O5′Manin both (IA) and (IB) [O3Xyl...O5′Maninternuclear distances = 2.7268 (16) and 2.6920 (17) Å, respectively], analogous to the inter-residue hydrogen bond detected between atoms O3Xyland O5′Galin (II). Exocyclic hydroxymethyl group conformation in the β-Manpresidue of (IA) isgauche–gauche, whereas that in the β-Manpresidue of (IB) isgauche–trans.

Disorder and conformational analysis of methyl β-D-galactopyranosyl-(1→4)-β-D-xylopyranoside

Methyl β-D-galactopyranosyl-(1→4)-β-D-xylopyranoside, C12H22O10, (II), crystallizes as colorless needles from water with positional disorder in the xylopyranosyl (Xyl) ring and no water molecules in the unit cell. The internal glycosidic linkage conformation in (II) is characterized by a ϕ′ torsion angle (C2′Gal—C1′Gal—O1′Gal—C4Xyl) of 156.4 (5)° and a ψ′ torsion angle (C1′Gal—O1′Gal—C4Xyl—C3Xyl) of 94.0 (11)°, where the ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH2OH) C atoms in the β-Xyl and β-Gal residues, respectively. By comparison, the internal linkage conformation in the crystal structure of the structurally related disaccharide, methyl β-lactoside [methyl β-D-galactopyranosyl-(1→4)-β-D-glucopyranoside], (III) [Stenutz, Shang & Serianni (1999).Acta Cryst.C55, 1719–1721], is characterized by ϕ′ = 153.8 (2)° and ψ′ = 78.4 (2)°. A comparison of β-(1→4)-linked disaccharides shows considerable variability in both ϕ′ and ψ′, with the range in the latter (∼38°) greater than that in the former (∼28°). Inter-residue hydrogen bonding is observed between atoms O3Xyland O5′Galin the crystal structure of (II), analogous to the inter-residue hydrogen bond detected between atoms O3Glcand O5′Galin (III). The exocyclic hydroxymethyl conformations in the Gal residues of (II) and (III) are identical (gauche–transconformer).

Quantum Constraints in π Systems: The Role of the Pauli Antisymmetry Principle for π Electronic Properties

It is demonstrated that the Pauli antisymmetry principle (PAP) is without influence in the π electron subspace of polyenes and (4n + 2) annulenes (n = 0, 1, 2...) as long as the hoppings are restricted to nearest-neighbour centers. Here the π electrons behave like a hard core bosonic (hcb) ensemble where fermionic on-site and bosonic intersite properties are combined. In 4n and (2n + 1) annulenes (n = 1,2, 3...) π electron jumps between the first and last ring atom lead to a Pauli antisymmetry-based destabilization. The second quantum constraint in fermionic systems is the Pauli exclusion principle (PEP). In the many-electron basis adopted in the present work it is possible to treat the PAP and PEP as two decoupled constraints. The electronic destabilization due to the PEP is enhanced with increasing size of the system. The influence of the PAP and PEP on the π electrons is discussed in terms of π energies and charge fluctuations. The model Hamiltonians adopted are of the Hückel molecular orbital (HMO) and Pariser-Parr-Pople (PPP) type. We suggest quantum statistical definitions of the quantities "aromaticity" and "antiaromaticity", qualitative descriptors which are widely employed in the chemical literature.

Polydeckerkomplexe mit μ,η5-2,3-Dihydro-1,3-diborolylnickel-Fragmenten als Stapeleinheiten / Polydecker Complexes with μ,η5-2,3-Dihydro-1,3-diborolylnickel Fragments as Stacking Units

Reactions of 2,3-dihydro-1,3-diboroles 6a–h with (C3H5)2Νi lead to µ,η5-2,3-dihydro-1,3-diborolylnickel triple-decker complexes 7a –h. By slow heating these oily, diamagnetic complexes in a rotating flask polycondensation with formation of black 8a–h as well as of bis(allyl)nickel and hexadiene occurs. The latter can be removed under reduced pressure. The constitution of the polymeric material follows from EXAFS studies. The Ni–Ni distance is 3,35 A, the ring atom Ni bonds are in the range of 2,13 to 2,15 A. Thermogravimetric measurements between 200 and 400°C show a mass loss of 20-40%, depending of the alkyl substituents of the heterocycle. In dynamic difference calorimetry an endothermic process occurs near 420°C. The powder conductivity of the amorphous, air-sensitive material is in the range of 10-2 S • cm-1. Doping with iodine or oxygen causes a decrease in the conductivity of these semi-conductors.

Molecular recognition IX. The synthesis of the H-type 2 human blood group determinant and congeners modified at the 6-position of the N-acetylglucosamine unit

The synthesis of the methyl glycosides of the H-type 2 human blood group determinant (α-L-Fuc-(1c → 2b)-β-D-Gal-(1b → 4a)-β-D-GlcNAc-OMe) and its 6a-deoxy, 6a-O-methyl, 6a-chloro-6a-deoxy, 6a-deoxy-6a-fluoro, 6a-amino-6a-deoxy, 6a-acetamido-6a-deoxy, and 6a-deoxy-6a-pivalamido congeners is reported. The compounds were prepared to test the hypothesis that the binding of the H-type 2 trisaccharide by the lectin I of Ulexeuropaeus requires OH-6a to become intramolecularly hydrogen bonded to the neighboring O-5a ring atom. The results obtained in the binding studies are reported in an accompanying publication (Spohr, Paszkiewicz-Hnatiw, Morishima, and Lemieux) where it is demonstrated that the formation of the intramolecular hydrogen bond is not required for effective binding. In view of the results reported in another accompanying paper (Nikrad, Beierbeck, and Lemieux), OH-6a most likely remains in contact with the aqueous phase near the periphery of the combining site. Keywords: N-acetylglucosamine derivatives, H-type 2 blood group determinant and congeners, oligosaccharide synthesis.